> On Oct 5, 2016, at 8:29 AM, Haravikk via swift-evolution
> <[email protected]> wrote:
>
>
>> On 4 Oct 2016, at 16:30, Tim Vermeulen via swift-evolution
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>> I think I agree with you. The postfix `!` operator is always shorthand for
>> `fatalError()` (and some more syntax), and it would fit nicely with
>> `default: fatalError()`.
>>
>> The Swift usage of `?` is indeed different than `default: break` would do,
>> so `switch?` wouldn’t convey the right message. I hadn’t given it enough
>> thought. I still think a shorthand for `default: break` would be _nice_, but
>> it surely shouldn’t change the `?` consistency, it also shouldn’t replace
>> the current `switch` (as exhaustiveness is very useful) and it’s probably
>> not worth introducing new syntax for.
>>
>>> On 4 Oct 2016, at 16:36, Xiaodi Wu <[email protected]
>>> <mailto:[email protected]>> wrote:
>>>
>>> There is a plausible argument for `switch!`, because it is not possible for
>>> the compiler to prove exhaustiveness in all circumstances where you might
>>> know it to be the case.
>>>
>>> However, I'd be very against `switch?`: it undermines the exhaustiveness
>>> guarantee of the switch statement and is wholly inconsistent with Swift
>>> usage of `?`, which indicates the possibility of an Optional. We simply
>>> don't need a new spelling for `default: break`.
>
> I agree with Tim; I'm a +1 for switch! for a convenient means of erroring
> out, but I think switch? is a bit too different from normal usage of the
> question-mark.
>
> One other alternative might be if there could be some kind of switch else
> syntax, kind of like a guard statement, allowing options on what to do? Only
> problem is how best to structure it, as the use of break might confusing as
> to its scope, like so:
>
> switch(foo) else break { // Break from the switch, or the enclosing
> block?
>
> So I'm not 100% on that. But it would mean that switch! would be a shorthand
> for switch else fatalError().
I will courteously jump in with a -1 for both switch! and switch?. I get how
pretty they are at first glance: they have symmetry with existing constructs.
However:
* I doubt they'll be used much and I don't think something should be added to
the language without measurable and consequential benefits.
* I don't think
`default: fatalError() // this should never happen, cases are exhaustive`
is a burden to type, in fact, I like how self-documenting it is, even if the
compiler sometimes guesses wrong -- in fact, I think the compiler *should*
guess wrong, especially on especially oddball case sets like `(.min ..< 0)` and
`(0 ... .max)`, let alone cases where you only want the even values within
those ranges.
* I do think that visually scanning for switch variants places a burden on code
readability. Unlike try? and try!, the switch!? statement will likely be lines
and lines away from where it impacts code. The place that best means "this
should never happen, cases are exhaustive" is the default case.
-- E
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